Carrier aggregation (CA) is a feature of Long Term Evolution (LTE) technology, where transmission between a base station, such as an evolved node B (eNB), and a user equipment (UE), such as a wireless handset, is performed using multiple component carriers (CCs) simultaneously. A component carrier on which a radio resource control (RRC) is originally setup is referred to as the primary CC for a UE, and the cell to which the primary CC is allocated is called the primary cell (PCell). The LTE network can add other cells to which other CCs are allocated, and these cells are called secondary cells (SCells).
When a queue of data is to be transmitted on multiple CCs, the eNB must decide how much of the data to transmit on each CC. Thus, the queue is split into multiple parts so that each part is assigned to a different CC. This is referred to as queue splitting. Component carriers can be scheduled sequentially. In such a case, queue splitting is trivial. Once scheduling of one CC is finalized, the number of bits that a queue is allowed to transmit on that CC can be subtracted from the total number of bits in the queue. Thus, the scheduler only sees the amount of bits remaining in the queue after scheduling the previous CCs. In contrast to sequential assignment of data to CCs, CCs can theoretically be assigned portions of data of the queue in parallel. However, with such parallel operation, the amount of bits to be assigned to each CC is not known, thereby potentially wasting resources by allocating too much to one CC and not enough to another CC.